Stent structures for use with valve replacements

ABSTRACT

The present embodiments provide a medical device for implantation in a patient comprising a stent and a valve. The stent comprises a proximal region comprising a cylindrical shape having a first outer diameter in an expanded state, and a distal region comprising a cylindrical shape having a second outer diameter in the expanded state. The second outer diameter is greater than the first outer diameter. A proximal region of the valve is at least partially positioned within the proximal region of the stent, and the distal region of the valve is at least partially positioned within one of tapered and distal regions of the stent. When implanted, the proximal region of the stent and the proximal region of the valve are aligned with a native valve, and the distal region of the valve is distally spaced-apart from the native valve.

RELATED APPLICATIONS

The application is a continuation application of U.S. patent applicationSer. No. 15/841,744, filed Dec. 14, 2017, which is a continuationapplication of U.S. patent application Ser. No. 13/286,407, filed Nov.1, 2011, which claims the benefit of priority under 35 U.S.C. § 120 ofU.S. Provisional Patent Application Ser. No. 61/410,540 filed Nov. 5,2010, all of which are hereby incorporated by reference in theirentireties.

BACKGROUND

The present embodiments relate to implantable medical devices, and moreparticularly to an implantable medical device for the repair of adamaged endoluminal valve, such as an aortic valve.

The aortic valve functions as a one-way valve between the heart and therest of the body. Blood is pumped from the left ventricle of the heart,through the aortic valve, and into the aorta, which in turn suppliesblood to the body. Between heart contractions the aortic valve closes,preventing blood from flowing backwards into the heart.

Damage to the aortic valve can occur from a congenital defect, thenatural aging process, and from infection or scarring. Over time,calcium may build up around the aortic valve causing the valve not toopen and close properly. Certain types of damage may cause the valve to“leak,” resulting in “aortic insufficiency” or “aortic regurgitation.”Aortic regurgitation causes extra workload for the heart, and canultimately result in weakening of the heart muscle and eventual heartfailure.

After the aortic valve becomes sufficiently damaged, the valve may needto be replaced to prevent heart failure and death. One current approachinvolves the use of a balloon-expandable stent to place an artificialvalve at the site of the defective aortic valve. Another currentapproach involves the positioning of an artificial valve at the site ofthe aortic valve using a self-expanding stent. The normal aortic valvefunctions well because it is suspended from above through its attachmentto the walls of the coronary sinus in between the coronary orifices, andit has leaflets of the perfect size and shape to fill the space in theannulus. However, these features may be difficult to replicate with anartificial valve. The size of the implantation site depends on theunpredictable effects of the balloon dilation of a heavily calcifiednative valve and its annulus. Poor valve function with a persistentgradient or regurgitation through the valve may result. In addition,different radial force considerations may be needed at the differentlocations for the prosthesis to optimally interact with a patient'sanatomy. Still further, it is important to reduce or prevent in-foldingor “prolapse” of an artificial valve after implantation, particularlyduring diastolic pressures.

BRIEF SUMMARY

The present embodiments provide a medical device for implantation in apatient. The medical device comprises a stent and a valve. The stentcomprises a proximal region comprising a cylindrical shape having afirst outer diameter when the stent is in an expanded state, and adistal region comprising a cylindrical shape having a second outerdiameter when the stent is in the expanded state. The second outerdiameter is greater than the first outer diameter.

In one embodiment, a plurality of closed cells are disposed around theperimeter of the proximal region of the stent, and another plurality ofclosed cells are disposed around the perimeter of the distal region ofthe stent. An overall length of each of the closed cells of the proximalregion of the stent is less than an overall length of each of the closedcells of the distal region of the stent when the stent is in theexpanded state.

In one embodiment, the stent further comprises a tapered region disposedbetween the proximal and distal regions. The tapered region transitionsthe stent from the first diameter to the second diameter. The taperedregion further comprises a plurality of closed cells. An overall lengthof each of the closed cells of the tapered region is greater than theoverall length of each of the closed cells of the proximal region andless than the overall length of each of the closed cells of the distalregion when the stent is in the expanded state.

A proximal region of the valve is at least partially positioned withinthe proximal region of the stent, and the distal region of the valve isat least partially positioned within one of the tapered and distalregions of the stent. When implanted, the proximal region of the stentand the proximal region of the valve are aligned with a native valve,and the distal region of the valve is distally spaced-apart from thenative valve.

Other systems, methods, features and advantages of the invention willbe, or will become, apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be within the scope of the invention, and be encompassed bythe following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereferenced numerals designate corresponding parts throughout thedifferent views.

FIGS. 1-2 are, respectively, side and perspective views of an exemplarystent structure in an expanded state.

FIG. 3 is a side view illustrating the stent structure of FIGS. 1-2 in acompressed state.

FIG. 4 is a side view of an exemplary integral barb of the stentstructure of FIGS. 1-2.

FIGS. 5-6 are perspective views of an exemplary aortic valve when noforces are imposed upon the valve.

FIG. 7 is a perspective view the aortic valve of FIGS. 5-6 duringsystole.

FIGS. 8-9 are side views illustrating a technique for coupling theaortic valve of FIGS. 5-7 to the stent structure of FIGS. 1-3.

FIG. 10 is a schematic showing the aortic prosthesis of FIG. 9 disposedwithin a patient's anatomy.

FIGS. 11-12 are, respectively, perspective views of an aortic valvecomprising suspension ties when no forces are imposed and duringdiastole.

FIG. 13 is a side view illustrating coupling of the aortic valve ofFIGS. 11-12 to the stent structure of FIGS. 1-3.

FIGS. 14-16 are, respectively, perspective views illustrating an aorticvalve comprising reinforcement strips when no forces are imposed, duringsystole and during diastole.

FIGS. 17-19 illustrate aortic valves comprising one or more alternativereinforcement strips.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

In the present application, the term “proximal” refers to a directionthat is generally closest to the heart during a medical procedure, whilethe term “distal” refers to a direction that is furthest from the heartduring a medical procedure.

Referring now to FIGS. 1-2, a first embodiment of a stent structure 20,which may be used in conjunction with an aortic valve prosthesis, isshown and described. The stent structure 20 may be used in conjunctionwith an aortic valve 120 to form a completed aortic valve prosthesis 10as shown in FIG. 9 below.

The stent structure 20 has a collapsed delivery state and an expandeddeployed state, and generally comprises a proximal region 30, a taperedregion 50, and a distal region 70, as shown in FIGS. 1-2. A pattern ofthe stent structure 20, depicted in a flattened and collapsed state, isshown in FIG. 3.

The stent structure 20 may be manufactured from a continuous cylinderinto which a pattern may be cut by a laser or by chemical etching toproduce slits in the wall of the cylinder. The resulting structure maythen be heat set to give it a desired final configuration. As shown inFIGS. 1-2, the final configuration may include a shape having a seriesof multiple closed cells.

The proximal region 30 of the stent structure 20 comprises a generallycylindrical shape having an expanded outer diameter d1. The proximalregion 30 is configured to be disposed at least partially within theaortic sinus, as shown in FIG. 10 below. By contrast, the distal region70 of the stent structure 20 comprises a generally cylindrical shapehaving an expanded outer diameter d2, and is configured to be disposedat least partially within the ascending aorta. The tapered region 50generally bridges the change from diameter d1 to diameter d2.

The proximal region 30 of the stent structure 20 may comprise multipleadjacent proximal apices 31. Each proximal apex 31 may comprise an endregion 32 having an integral barb 33 formed therein, as shown in FIG. 4.The barb 33 may be formed by laser cutting a desired barb shape into theend regions 32. A slit 34 therefore is formed into each end region 32after the desired barb shape is formed, as shown in FIG. 4. Once thedesired barb shape is cut, a main body of the barb 33 may be bent in aradially outward direction with respect to the end region 32. The anglemay comprise any acute angle, or alternatively may be substantiallyorthogonal or obtuse. If desired, the barb 33 may be sharpened, forexample, by grinding the tip of the barb, to facilitate engagement at atarget tissue site.

Referring still to FIGS. 1-2, the proximal region 30 of the stentstructure 20 further may comprise a plurality of closed cells 35 formedby multiple angled strut segments. In one example, four angled strutsegments 36, 37, 38 and 39 form one closed cell 35, as shown in FIG. 1.In this example, a first proximal apex 31 extends distally and splitsinto first and second angled strut segments 36 and 37, respectively,which are joined to one another at a junction 41. Further, third andfourth angled strut segments 38 and 39 are joined at the junction 41 andextend distally therefrom, as shown in FIG. 1. In a compressed state,the angled strut segments 36-39 of the cell 35 may be compressed suchthat they are substantially parallel to one another.

The first and second angled strut segments 36 and 37 each generallycomprise a length L1, and each are generally disposed at an angle α1relative to a longitudinal axis L of the stent structure 20, as shown inFIG. 1. The third and fourth angled strut segments 38 and 39 eachgenerally comprise a length L2 and each are generally disposed at anangle α2 relative to the longitudinal axis L, as shown in FIG. 1. Theclosed cell 35 comprises a total length L3, representing the combinedlengths L1 and L2, as shown in FIG. 1.

In this example, the length L1 of the first and second angled strutsegments 36 and 37 is greater than the length L2 of the third and fourthangled strut segments 38 and 39. In one embodiment, the length L1 may beabout 1.5 to about 4.0 times greater than the length L2.

Moreover, a cross-sectional area of the first and second angled strutsegments 36 and 37 may be greater than a cross-sectional area of thethird and fourth angled strut segments 38 and 39. In one embodiment, thecross-sectional area of the first and second angled strut segments 36and 37 is about 4 times greater than the cross-sectional area of thethird and fourth angled strut segments 38 and 39. The increasedcross-sectional area of the first and second angled strut segments 36and 37 causes these segments to primarily provide the radial forcewithin the closed cells 35, while the third and fourth angled strutsegments 38 and 39 are mainly intended for connecting adjacent closedcells 35 and 55 a, instead of providing significant radial force.

Further, in this example, the angle α2 of the third and fourth angledstrut segments 38 and 39 is greater than the angle α1 of the first andsecond angled strut segments 36 and 37. Since the first and secondangled strut segments 36 and 37 are primarily providing the radialforce, the angle α1 is selected to achieve the desired radial force,while as noted above, the third and fourth angled strut segments 38 and39 are mainly intended for connecting adjacent closed cells 35 and 55 a,and therefore yield a different angle α2 for this different primarypurpose. In one embodiment, the angle α2 may be about 1.2 to 4.0 timesgreater than the angle α1.

Overall, given the relative lengths and angle configurations describedabove, each closed cell 35 comprises a generally spade-shapedconfiguration, as shown in FIGS. 1-2. As will be apparent, however, therelative lengths and angles may be greater or less than depicted and/orprovided in the exemplary dimensions disclosed herein.

The pattern of angled strut segments 36-39 may be repeated around thecircumference of the proximal region 30 of the stent structure 20. Inthis manner, the stent structure 20 may be formed into a continuous,generally cylindrical shape. In one example, ten proximal apices 31 andten closed cells 35 are disposed around the circumference of theproximal region 30, although greater or fewer proximal apices and closedcells may be provided to vary the diameter and/or radial forcecharacteristics of the stent.

The proximal region 30 may be flared slightly relative to thelongitudinal axis L. In one example, a proximal end of each apex 31 maybe bowed outward relative to a distal end of the same apex 31. Such aflaring may facilitate engagement with the aortic sinus when implanted.

Referring still to FIGS. 1-2, the tapered region 50 also comprises aplurality of closed cells. In this example, four different closed cells55 a, 55 b, 55 c and 55 d are provided along the length of the taperedregion 50. Each of the closed cells 55 a-55 d may comprise a slightlydifferent shape, as shown in FIGS. 1-2. In this example, ten of eachseries of closed cells 55 a-55 d are disposed around the circumferenceof the tapered region 50, and the diameter of the tapered region 50increases from the outer diameter d1 to the outer diameter d2.

In one example, four angled strut segments 56, 57, 58 and 59 form oneclosed cell 55 b, as shown in FIG. 1. The first and second angled strutsegments 56 and 57 each generally comprise a length L4 and each aregenerally disposed at an angle relative to the longitudinal axis L thatmay be about the same as, or slightly greater or less than, the angleα1. The third and fourth angled strut segments 58 and 59 each generallycomprise a length L5 and each are generally disposed at an anglerelative to the longitudinal axis L that may be about the same as, orslightly greater or less than, the angle α2. The closed cell 55 bcomprises a total length L6, representing the combined lengths L4 andL5, as shown in FIG. 1.

In this example, the length L4 of the first and second angled strutsegments 56 and 57 is greater than the length L5 of the third and fourthangled strut segments 58 and 59. In one embodiment, the length L4 may beabout 1.1 to about 4 times greater than the length L5.

Further, in this example, the total length L6 of the closed cell 55 b ofthe tapered region 50 is greater than the total length L3 of the closedcell 35 of the proximal region 30, as shown in FIG. 1. Moreover, in oneexample, the length of one or more individual struts of the taperedregion 50, e.g., first and second angled strut segments 56 and 57 havinglength L4, may be longer than the total length L3 of the closed cell 35of the proximal region 30.

The distal region 70 similarly comprises a plurality of closed cells. Inthis example, two different closed cells 75 a and 75 b are providedalong the length of the distal region 70. The closed cells 75 a and 75 bmay comprise a different shape relative to one another, as shown inFIGS. 1-2. In this example, ten of each series of closed cells 75 a and75 b are disposed around the circumference of the distal region 70 toform the overall outer diameter d2.

In one example, the most distal closed cell 75 b comprises four angledstrut segments 76, 77, 78 and 79, as shown in FIG. 1. The first andsecond angled strut segments 76 and 77 each generally comprise a lengthL7 and each are generally disposed at an angle relative to thelongitudinal axis L that may be about the same as, or slightly greateror less than, the angle α1. The third and fourth angled strut segments78 and 79 each generally comprise a length L9 and each are generallydisposed at an angle relative to the longitudinal axis L that may beabout the same as, or slightly greater or less than, the angle α2.

Further, a barbed region 80 having a barb 83 is disposed between theangled strut segments, as shown in FIG. 1. The barb 83 of the barbedregion 80 may be formed integrally in the same manner as the barb 33 ofthe proximal region 30, as shown in FIG. 4, but preferably faces in aproximal direction. The barbed region 80 is generally parallel to thelongitudinal axis L of the stent structure 20 and comprises a length L8.The cell 55 b comprises a total length L10, representing the combinedlengths L7, L8 and L9, as shown in FIG. 1.

In this example, the length L7 of the first and second angled strutsegments 76 and 77 is greater than the length L9 of the third and fourthangled strut segments 78 and 79. In one embodiment, the length L7 may beabout 1.1 to about 4.0 times greater than the length L9.

Further, in this example, the total length L10 of the closed cell 75 bof the distal region 70 is greater than the total length L6 of theclosed cell 55 b of the tapered region 50, which in turn is greater thanthe total length L3 of the closed cell 35 of the proximal region 30, asshown in FIG. 1. Therefore, the lengths of individual closed cellsincrease along the stent structure from a proximal end 22 to a distalend 24 of the stent structure 20.

Advantageously, since the lengths of individual closed cells generallyincrease along the stent structure 20 from the proximal end 22 to thedistal end 24, the forces imposed by the stent structure 20 alongdifferent regions may be varied for a patient's anatomy. Radial forceand stiffness are a function of the individual cell lengths. Therefore,in the example of an aortic valve replacement, a relatively short lengthL3 of the closed cell 35 of the proximal region 30 yields a relativelyhigh radial force imposed upon the aortic sinus to allow for an enhancedand rigid attachment at this location. Conversely, a relatively longlength L10 of the closed cell 75 b of the distal region 70 yields arelatively low radial force imposed upon the ascending aorta, therebyfacilitating a flexible contour at the distal region 70 that does notadversely impact the ascending aorta 105.

Additionally, radial force and stiffness are a function of the strutangles. In the example of FIGS. 1-2, the individual struts 36 and 37 ofthe proximal region 30 may have a shallower strut angle relative to theindividual struts 76 and 77 of the distal region 70, i.e., theindividual struts 36 and 37 may be more perpendicular to thelongitudinal axis L of the device. Therefore, the angles of theindividual struts 36 and 37 may contribute to a higher radial force atthe proximal region 30 relative to the individual struts 76 and 77 ofthe distal region 70.

Further, an increased strut width may be provided at the proximal region30 to promote a higher radial force relative to the strut width at thedistal region 70. In sum, the stent structure 20 has different radialforce properties at its proximal and distal regions 30 and 70 thatbeneficially interact with their associated regions into which they areimplanted, e.g., the aortic sinus and the ascending aorta, respectively.

In one embodiment, the lengths of individual cells may always increaserelative to one another moving in a proximal to distal direction, i.e.,each closed cell has an overall length that is greater than a length ofevery other closed cell that is disposed proximally thereof. In otherembodiments, adjacent cells may comprise about the same length, or aproximal cell may comprise a lesser length than an adjacent distal cell.Therefore, while the lengths of individual angled strut segmentsgenerally increase in a proximal to distal direction, it is possiblethat some of the individual angled strut segments of a more distalregion may be smaller than a more proximally oriented region.

Expansion of the stent structure 20 is at least partly provided by theangled strut segments, which may be substantially parallel to oneanother in a compressed state of FIG. 3, but may tend to bow outwardaway from one another in the expanded state shown in FIGS. 1-2. Thestent structure 20 may be formed from any suitable material, and formedfrom a laser-cut cannula. The stent structure 20 has a reduced diameterdelivery state so that it may be advanced to a target location within avessel or duct. Further, the struts of the stent may comprise asubstantially flat wire profile or may comprise a rounded profile. Asbest seen in FIGS. 1-2, the struts of the stent generally comprise aflat wire profile in this example.

The stent structure 20 may be manufactured from a super-elasticmaterial. Solely by way of example, the super-elastic material maycomprise a shape-memory alloy, such as a nickel titanium alloy(nitinol). If the stent structure 20 comprises a self-expanding materialsuch as nitinol, the stent may be heat-set into the desired expandedstate, whereby the stent structure 20 can assume a relaxed configurationin which it assumes the preconfigured first expanded inner diameter uponapplication of a certain cold or hot medium. Alternatively, the stentstructure 20 may be made from other metals and alloys that allow thestent structure 20 to return to its original, expanded configurationupon deployment, without inducing a permanent strain on the material dueto compression. Solely by way of example, the stent structure 20 maycomprise other materials such as stainless steel, cobalt-chrome alloys,amorphous metals, tantalum, platinum, gold and titanium. The stentstructure 20 also may be made from non-metallic materials, such asthermoplastics and other polymers.

It is noted that some foreshortening of the stent structure 20 may occurduring expansion of the stent from the collapsed configuration of FIG. 3to the expanded deployed state of FIGS. 1-2. Since the proximal region30 of the stent structure 20 is deployed first, it is expected that suchforeshortening is not problematic since a precise landing area of thedistal region 70 within the ascending aorta is generally not needed, solong as solid contact is achieved.

Moreover, in order to reduce migration of the stent structure whenimplanted at a target site, it is preferred that the barbs 33 of theproximal region 30 are oriented in a distally-facing direction, whereasthe barbs 83 of the distal region 70 are oriented in a proximally-facingdirection. However, additional or fewer barbs may be disposed at variouslocations along the stent structure 20 and may be oriented in the sameor different directions. Moreover, integral and/or externally attachedbarbs may be used.

Referring now to FIGS. 5-7, a first embodiment of an aortic valve 120,which may be used in conjunction with the stent structure 20 to form anaortic prosthesis, is shown and described. The aortic valve 120generally comprises proximal and distal regions 130 and 170,respectively, and a tapered region 150 disposed therebetween. The aorticvalve 120 comprises a delivery state in which it may be compressed forpercutaneous implantation along with the stent structure 20, and furthercomprises different states during systole and diastole. Generally,antegrade flow opens the aortic valve 120 while retrograde flow closesthe aortic valve 120. In the phase of systole for the aortic valve 120,depicted in FIG. 7, blood may flow through the opposing flat surfaces172 and 174 at the distal end 170 of the aortic valve 120. In the phaseof diastole for the aortic valve 120, opposing flat surfaces 172 and 174at the distal end 170 of the aortic valve 120 are generally adjacent toone another to inhibit blood flow back through the valve.

The proximal region 130 generally comprises a cylindrical body having anouter diameter that is approximately equal to, or just less than, anexpanded inner diameter of the proximal region 30 of the stent structure20. In one method of manufacture, shown in FIGS. 8-9 and describedbelow, the aortic valve 120 is disposed generally within the stentstructure 20 such that the proximal region 130 is at least partiallyaligned with the proximal region 30 of the stent structure 20.

The tapered region 150 of the aortic valve 120 may comprise two opposingflat surfaces 152 and 154, as shown in FIGS. 5-6. The opposing flatsurfaces 152 and 154 generally each comprise a proximal portion 156 inthe form of a curved area that reduces the diameter of the proximalregion 130, and a distal portion 157 in the form of a wide flat panelthat transitions into the distal region 170, as shown in FIGS. 5-6.

The distal region 170 of the aortic valve 120 may comprise a generallyrectangular profile from an end view, i.e., looking at the device from adistal to proximal direction. The distal region 170 comprises theopposing flat surfaces 172 and 174 noted above, which are separated bynarrower flat sides 175 a and 175 b, as shown in FIGS. 5-6. The opposingflat surfaces 152 and 154 of the tapered region 150 generally transitioninto the opposing flat surfaces 172 and 174 of the distal region 170,respectively. The opposing flat surfaces 152 and 154 of the taperedregion 150 are angled relative to both the proximal region 130 and thedistal region 170, as shown in FIGS. 5-6.

The aortic valve 120 may comprise a biocompatible graft material ispreferably non-porous so that it does not leak under physiologic forces.The graft material may be formed of Thoralon® (Thoratec® Corporation,Pleasanton, Calif.), Dacron® (VASCUTEK® Ltd., Renfrewshire, Scotland,UK), a composite thereof, or another suitable material. Preferably, thegraft material is formed without seams. The tubular graft can be made ofany other at least substantially biocompatible material including suchfabrics as other polyester fabrics, polytetrafluoroethylene (PTFE),expanded PTFE, and other synthetic materials. Naturally occurringbiomaterials are also highly desirable, particularly a derived collagenmaterial known as extracellular matrix. An element of elasticity may beincorporated as a property of the fabric or by subsequent treatmentssuch as crimping.

Referring to FIGS. 8-9, in one method of manufacture, the aortic valve120 is disposed generally within the stent structure 20 such that theproximal region 130 of the aortic valve 120 is at least partiallyaligned with the proximal region 30 of the stent structure 20. Aproximal attachment portion 132 of the aortic valve 120 having a lengthx is disposed proximal to the proximal apices 31 of the stent structure20, as shown in FIG. 8, then the proximal attachment portion 132 isfolded externally over the proximal apices 31, as shown in FIG. 9. Theproximal attachment portion 132 then may be sutured or otherwiseattached to the proximal apices 31 and/or any of the angled strutsegments 36-39, thereby securing a portion of the aortic valve 120 tothe stent structure 20 to form a complete aortic prosthesis 10, asdepicted in FIG. 9. The barbs 33 of the stent structure 20 may protrudethrough the fabric of the proximal attachment portion 132 for engagementwith targeted tissue.

When the aortic valve 120 is coupled to the stent structure 20 as shownin FIGS. 8-9, the distal region 170 of the aortic valve 120 may extendwithin the tapered region 50 and/or the distal region 70 of the stentstructure 20, and may be generally centrally disposed therein, althoughthe exact positioning of distal region 170 of the aortic valve 120relative to the stent structure 20 may be varied as needed. Moreover,one or more reinforcement members, described generally in FIGS. 11-19below, may be coupled to the aortic valve 120 and/or the stent structure20 to enhance structural integrity and/or functionality of the aorticprosthesis 10.

Advantageously, the distal region 170 of the aortic valve 120 isdisposed within the tapered region 50 and/or the distal region 70 of thestent structure 20, which are positioned in the proximal ascendingthoracic aorta above (distal to) the annulus and above the native aorticvalve. Previous valves are designed to occupy the aortic annulus;however, the unpredictable shape and diameter of the aortic annulusmakes the valve unpredictable in shape and diameter, leading toasymmetric replacement valve movement, leakage and reduced durability.In short, by moving the distal region 170 of the aortic valve 120 to adistally spaced-apart location relative to the native aortic valve,i.e., the unpredictable shape and diameter of the aortic annulus haveless impact upon the spaced-apart distal region 170 of the aortic valve120, and therefore the distal region 170 is less subject to asymmetricvalve movement and leakage, and may have increased durability.

The shape and dimensions of the proximal and tapered regions 130 and 150can vary without significantly affecting flow or valve function at thedistal region 170. While the distal region 170 of the valve 120 is shownhaving a generally rectangular shape, a tricuspid-shaped distal regionof the valve may be provided, in which case the tapered region 150 maybe omitted or altered to accommodate such a tricuspid-shaped distalregion.

Referring now to FIG. 10, a partial cut-away view of a heart 102 and anaorta 104 are shown. The heart 102 may comprise an aortic valve 106 thatdoes not seal properly. This defect of the aortic valve 106 allows bloodto flow from the aorta 104 back into the left ventricle, leading to adisorder known as aortic regurgitation. Also shown in FIG. 10 are abrachiocephalic trunk 112, a left common carotid artery 114, and a leftsubclavian artery 116. A portion of the aorta 104 referred to herein asan ascending aorta 105 is shown located between the aortic valve 106 andthe brachiocephalic trunk 112. A patient's coronary arteries 117 and 118are located distal to the aortic valve 106.

The aortic prosthesis 10 is introduced into a patient's vascular system,delivered, and deployed using a deployment device, or introducer. Thedeployment device delivers and deploys the aortic prosthesis 10 withinthe aorta at a location to replace the aortic valve 106, as shown inFIG. 10. The deployment device may be configured and sized forendoluminal delivery and deployment through a femoral cut-down. Theaortic prosthesis 10, with the stent structure 20 in a radiallycollapsed state, may be inserted into a delivery catheter usingconventional methods. In addition to a delivery catheter, various othercomponents may need to be provided in order to obtain a delivery anddeployment system that is optimally suited for its intended purpose.These include and are not limited to various outer sheaths, pushers,trigger wires, stoppers, wire guides, and the like. For example, theZenith® Thoracic Aortic Aneurysm Endovascular Graft uses a deliverysystem that is commercially available from Cook Inc., Bloomington, Ind.,and may be suitable for delivering and deploying an aortic prosthesis inaccordance with the present embodiments.

In one aspect, a trigger wire release mechanism is provided forreleasing a retained end of the stent structure 20 of the aorticprosthesis 10. Preferably, the trigger wire arrangement includes atleast one trigger wire extending from a release mechanism through thedeployment device, and the trigger wire is engaged with selectedlocations of the stent structure 20. Individual control of thedeployment of various regions of the stent structure 20 enables bettercontrol of the deployment of the aortic prosthesis 10 as a whole.

While the stent structure 20 is generally described as a self-expandingframework herein, it will be appreciated that a balloon-expandableframework may be employed to accomplish the same functionality. If aballoon-expandable stent structure is employed, then a suitable ballooncatheter is employed to deliver the aortic prosthesis as generallyoutlined above. Optionally, after deployment of a self-expanding stentstructure 20, a relatively short balloon expandable stent may bedelivered and deployed inside of the proximal region 30 of the stentstructure 20 to provided added fixation at the location of the aorticsinus.

Upon deployment, the aortic prosthesis 10 is positioned as generallyshown in FIG. 10. Advantageously, as noted above, since the lengths ofindividual cells generally increase along the stent structure 20 fromthe proximal end 22 to the distal end 24, a relatively high radial forceis imposed by the closed cells 35 of the proximal region 30 upon theaortic sinus 106 to allow for an enhanced and rigid attachment at thislocation. Conversely, a relatively low radial force is imposed by theclosed cells 75 a and 75 b of the distal region 70 upon the ascendingaorta 105, thereby facilitating a flexible contour at the distal regionthat does not adversely impact the ascending aorta 105.

When the aortic prosthesis 10 is implanted, sufficient flow into thecoronary arteries 117 and 118 is maintained during retrograde flow. Inparticular, after blood flows through the distal region 170 of theaortic valve 120, blood is allowed to flow adjacent to the outside ofthe tapered central region 150 of the aortic valve 120 and into thecoronary arteries 117 and 118, i.e., through the open individual cellsof the stent structure 20.

Further, if the barbs 33 are disposed at the proximal region 30, thebarbs 33 promote a secure engagement with the aortic sinus 106.Similarly, the barbs 83 at the distal region 70 promote a secureengagement with the ascending aorta 105. In the event barbs are omitted,the proximal and distal regions 30 and 70 may be configured so that theradial forces exerted upon the coronary sinus 105 and the ascendingaorta 105, respectively, are enough to hold the stent structure 20 inplace.

The shape, size, and dimensions of each of the members of the aorticprosthesis 10 may vary. The size of a preferred prosthetic device isdetermined primarily by the diameter of the vessel lumen (preferably fora healthy valve/lumen combination) at the intended implant site, as wellas the desired length of the overall stent and valve device. Thus, aninitial assessment of the location of the natural aortic valve in thepatient is determinative of several aspects of the prosthetic design.For example, the location of the natural aortic valve in the patientwill determine the dimensions of the stent structure 20 and the aorticvalve 120, the type of valve material selected, and the size ofdeployment vehicle.

After implantation, the aortic valve 120 replaces the function of therecipient's native damaged or poorly performing aortic valve. The aorticvalve 120 allows blood flow when the pressure on the proximal side ofthe aortic valve 120 is greater than pressure on the distal side of thevalve. Thus, the artificial valve 120 regulates the unidirectional flowof fluid from the heart into the aorta.

Referring now to FIGS. 11-19, various reinforcement members aredescribed that may be coupled to the aortic valve 120 and/or the stentstructure 20 to enhance structural integrity and/or functionality of theaortic prosthesis 10. The normal, native aortic valve is suspended fromabove through its attachment to the walls of the coronary sinus, andsuspended aortic valves resist the forces created by diastolic pressureon closed leaflets through attachment to downstream support. The variousreinforcement members of FIGS. 11-19 are intended to reinforce theaortic valve 120, and in particular, prevent in-folding or “prolapse” ofthe valve during diastole.

In FIGS. 11-13, a first embodiment of reinforcement members comprises aplurality of suspension ties 180 a-180 d that are coupled between thetapered region 150 of the aortic valve 120 and the tapered region 50 ofthe stent structure 20. In the phase of systole for the aortic valve120, blood may flow through the opposing flat surfaces 172 and 174 atthe distal end 170 of the aortic valve 120, and the suspension ties 180a-180 d are relatively slack allowing for normal opening of the aorticvalve 120. In the phase of diastole for the aortic valve 120, opposingflat surfaces 172 and 174 at the distal end 170 of the aortic valve 120are generally adjacent to one another to inhibit blood flow back throughthe valve, while the suspension ties 180 a-180 d become more taut andprevent prolapse of the aortic valve 120 when retrograde flow is imposedupon the exterior surfaces of the valve, as depicted in the finiteelement analysis simulation of FIG. 12. In effect, the suspension ties180 a-180 d advantageously provide a safety mechanism by which prolapseis avoided during retrograde flow.

In the example of FIGS. 11-13, the suspension ties 180 a-180 d may bemolded into the aortic valve 120 in the manner that fiber reinforcementsare molded into a graft structure, and further may be coupled to one ormore struts of the stent structure 20 using sutures 198 or anothersuitable coupling member that does not impede expansion of the stentstructure 20. While first ends of the suspension ties 180 a-180 d areshown coupled to the tapered region 150 of the aortic valve 120, theymay alternatively, or additionally, be coupled to another location, suchas the distal region 170. Similarly, while second ends of the suspensionties 180 a-180 d are shown coupled to the tapered region 50 of the stentstructure 20, they may alternatively, or additionally, be coupled toanother location, such as the distal region 70. While four exemplarysuspension ties 180 a-180 d are shown, greater or fewer suspension tiesmay be used, and their positioning may be varied as noted above, toachieve the desired functionality and reduce potential prolapse of theaortic valve 120.

The angles α3 of the suspension ties 180 a-180 d relative to thelongitudinal axis L, as shown in FIG. 13, may be between about 40-80degrees when relatively slack. However, it will be appreciated theangles α3 may be greater or less than what is depicted in FIG. 13.

In one example, the suspension ties 180 a-180 d comprise a thickness ofbetween about 0.002-0.02 inches, and are molded into a Thoralon® orDacron® coating. Other materials may be used, so long as the suspensionties 180 a-180 d are non-thrombogenic, or coated with a non-thrombogenicmaterial.

Advantageously, in the case where the tapered or distal regions 150 and170 of the aortic valve 120 are supported from above through attachmentto the stent structure 20 at a location in the ascending thoracic aorta,the aortic valve 120 can therefore be as long as necessary for optimalvalve function, even if it is of a simple bicuspid design. In otherwords, the length of the aortic valve 120 can be varied such that thedistal region 170 of the aortic valve 120 is positioned at the desiredlocation within the ascending thoracic aorta spaced-apart from thenative aortic annulus.

Referring now to FIGS. 14-19, alternative embodiments of reinforcementmembers are shown and described that comprise one or more reinforcementstrips. In FIGS. 14-16, a first reinforcement strip 185 a generallyextends between a portion of the proximal region 130, through oneopposing flat surface 152 of the tapered region 150, and to one opposingflat surface 172 of the distal region 170, as shown in FIGS. 14-16. Asecond reinforcement strip 185 b is disposed about 90 degrees apart fromthe first reinforcement strip 185 a, and generally extends between aportion of the proximal region 130 towards one of the narrower flatsides 175 a. A third reinforcement strip 185 c is disposed about 90degrees apart from the first reinforcement strip 185 a, and generallyextends between a portion of the proximal region 130, through oneopposing flat surface 154 of the tapered region 150, and to one opposingflat surface 174 of the distal region 170. A fourth reinforcement stripis obscured in FIGS. 14-16 but may be disposed about 90 degrees apartfrom the second reinforcement strip 185 b and is a mirror image thereof.

In the phase of systole for the aortic valve 120, shown in FIG. 15,blood may flow through the opposing flat surfaces 172 and 174 at thedistal end 170 of the aortic valve 120, and the reinforcement strips 185a-185 c are relatively flat allowing for normal opening of the aorticvalve 120. In the phase of diastole for the aortic valve 120, shown inFIG. 16, opposing flat surfaces 172 and 174 at the distal end 170 of theaortic valve 120 are generally adjacent to one another to inhibit bloodflow back through the valve, while the reinforcement strips 185 a-185 dmay become bowed radially inward along the tapered region 150 to preventprolapse of the aortic valve 120 when retrograde flow is imposed uponthe exterior surfaces of the valve. In one example, the reinforcementstrips 185 a-185 c may snap between the states depicted in FIGS. 15-16during systole and diastole, respectively, when the associated pressuresare imposed upon the aortic valve 120. In effect, the reinforcementstrips 185 a-185 c advantageously provide a safety mechanism by whichprolapse is avoided during retrograde flow.

In one example, the reinforcement strips 185 a-185 c of FIGS. 14-16comprise stainless steel or nitinol, though any suitable material toperform such functions may be used. The reinforcement strips maycomprise a thickness of about 0.002 to about 0.010 inches and may bemolded into the material of the aortic valve 120, or coupled externallythereto.

In FIGS. 17-19, various alternative reinforcement strips are depicted.In FIG. 17, at least one elliptical reinforcement strip 190 is coupledto a portion of the proximal region 130 of the aortic valve 120 andextends distally into the tapered region 150, positioned generallybetween the opposing flat surfaces 152 and 154 of the tapered region150. In FIG. 18, a first elliptical reinforcement strip 191 is coupledentirely to the flat surface 152 of the tapered region 150, while asecond longitudinal reinforcement strip 192 extends between the proximalregion 130 and tapered region 150 and is positioned generally betweenthe opposing flat surfaces 152 and 154 of the tapered region 150. InFIG. 19, a diamond-shaped reinforcement strip 193 is coupled between theproximal region 130 and the flat surface 152 of the tapered region 150.Like the reinforcement strips 185 a-185 c of FIGS. 14-16, thereinforcement strips 190-193 of FIGS. 17-19 may snap between two statesduring systole and diastole. In each of the embodiments of FIGS. 17-19,the reinforcement strips 190-193 advantageously provide a safetymechanism by which prolapse is avoided during retrograde flow. Whilevarious exemplary reinforcement strip shapes and locations are shown inFIGS. 14-19, the shapes and locations of the reinforcement strips may bevaried, and greater or fewer strips may be used, without departing fromthe spirit of the present embodiments.

In still further embodiments, the stent structure 20 shown herein may beused in connection with different aortic valves, beside the aortic valve120. Solely by way of example, and without limitation, variousartificial valve designs may have two or three membranes, and may bearranged in various shapes including slots and flaps that mimic thenatural functionality of an anatomical valve. Conversely, the aorticvalve 120 shown herein may be used in conjunction with different stentstructures.

While various embodiments of the invention have been described, theinvention is not to be restricted except in light of the attached claimsand their equivalents. Moreover, the advantages described herein are notnecessarily the only advantages of the invention and it is notnecessarily expected that every embodiment of the invention will achieveall of the advantages described.

1. A medical device for implantation in a patient, the medical devicecomprising: a stent comprising: a proximal region comprising acylindrical shape having a first outer diameter when the stent is in anexpanded state; a distal region comprising a cylindrical shape having asecond outer diameter when the stent is in the expanded state, where thesecond outer diameter is greater than the first outer diameter; atapered region disposed between the proximal and distal regions, wherethe tapered region transitions the stent from the first diameter to thesecond diameter; and a valve coupled to at least a portion of the stent,the valve having proximal and distal regions, where the proximal regionof the valve is at least partially positioned within the proximal regionof the stent and the distal region of the valve is at least partiallypositioned within one of the tapered and distal regions of the stent. 2.The medical device of claim 1 where, when implanted, the proximal regionof the stent and the proximal region of the valve are aligned with anative valve, and the distal region of the valve is distallyspaced-apart from the native valve.
 3. The medical device of claim 1further comprising a plurality of closed cells disposed around theperimeter of the proximal region of the stent, and another plurality ofclosed cells disposed around the perimeter of the distal region of thestent.
 4. The medical device of claim 3 where the tapered region furthercomprises a plurality of closed cells, where an overall length of eachof the closed cells of the tapered region is greater than an overalllength of each of the closed cells of the proximal region of the stentand less than an overall length of each of the closed cells of thedistal region of the sent when the stent is in the expanded state. 5.The medical device of claim 3 where the plurality of closed cells of theproximal region of the stent comprise a higher radial force relative tothe plurality of closed cells of the distal region of the stent when thestent is in the expanded state.
 6. The medical device of claim 3 whereat least one of the closed cells of the distal region of the stentcomprises four angled strut segments, and where two of the angled strutsegments comprise a greater length relative to the other two angledstrut segments within the closed cell.
 7. The medical device of claim 1where the proximal region of the valve comprises a cylindrical body, andthe distal region of the valve has a generally rectangular shapecomprising opposing flat surfaces that are separated by narrower flatsides, where the opposing flat surfaces at the distal end of the valveallow fluid flow therethrough during antegrade flow and are generallyadjacent to one another to inhibit blood flow through the valve duringretrograde flow.
 8. The medical device of claim 1 where the proximalregion of the stent comprises a plurality of proximal apices, where atleast one of the proximal apices has an end region having an integralbarb formed therein, where the plurality of closed cells of the proximalregion are disposed distal to the plurality of proximal apices.
 9. Amedical device for implantation in a patient, the medical devicecomprising: a stent having proximal and distal regions, and furthercomprising delivery and expanded states; a plurality of closed cellsdisposed at various locations between the proximal and distal regions ofthe stent, where each closed cell has an overall length, when the stentis in the expanded state, that is greater than a length of every otherclosed cell that is disposed proximally thereof; and a valve coupled toat least the proximal region of the stent.
 10. The medical device ofclaim 9, where the stent comprises at least three longitudinal regionsin which a plurality of closed cells are disposed around a perimeter ofthe stent, where the first longitudinal region is disposed proximal tothe second longitudinal region, and the second longitudinal region isdisposed proximal to the third longitudinal region, where an overalllength of each of the closed cells of the first longitudinal region isless than an overall length of each of the closed cells of the secondlongitudinal region, and where the overall length of each of the closedcells of the second longitudinal region is less than an overall lengthof each of the closed cells of the third longitudinal region.
 11. Themedical device of claim 9 where a plurality of closed cells disposedaround a perimeter of the proximal region of the stent comprise a higherradial force relative to a plurality of closed cells disposed around aperimeter of the distal region of the stent.
 12. The medical device ofclaim 9 where at least one of the closed cells comprises four angledstrut segments, and where two of the angled strut segments comprise agreater length relative to the other two angled strut segments withinthe closed cell.
 13. The medical device of claim 9 where at least one ofthe closed cells comprises four angled strut segments, and where two ofthe angled strut segments comprise a first width, which is greater thana second width of the other two angled strut segments within the closedcell.
 14. The medical device of claim 9 where the proximal region of thestent comprises a cylindrical shape having a first outer diameter whenthe stent is in the expanded state, and where the distal region of thestent comprises a cylindrical shape having a second outer diameter whenthe stent is in the expanded state, where the second outer diameter isgreater than the first outer diameter, the stent further comprising: atapered region disposed between the proximal and distal regions, wherethe tapered region transitions the stent from the first outer diameterto the second outer diameter.
 15. A medical device for implantation in apatient, the medical device comprising: a stent comprising: a proximalregion comprising a cylindrical shape having a first outer diameter whenthe stent is in an expanded state; a distal region comprising acylindrical shape having a second outer diameter when the stent is inthe expanded state, where the second outer diameter is greater than thefirst outer diameter; a tapered region disposed between the proximal anddistal regions, where the tapered region transitions the stent from thefirst diameter to the second diameter; and a valve having proximal anddistal regions, where the proximal region of the valve is positioned atleast partially within the proximal region of the stent, and where atleast a portion of the valve is mechanically coupled to one of thetapered and distal regions of the stent.
 16. The medical device of claim15 where an overall length of each of a plurality of closed cells of theproximal region of the stent is less than an overall length of each of aplurality of closed cells of the distal region of the stent when thestent is in the expanded state.
 17. The medical device of claim 16 wherethe tapered region of the stent further comprises plurality of closedcells, where an overall length of each of the closed cells of thetapered region is greater than the overall length of each of the closedcells of the proximal region of the stent and less than an overalllength of each of the closed cells of the distal region of the stent.18. The medical device of claim 16 where at least one of the closedcells of the proximal region of the stent comprises four angled strutsegments, and where two of the angled strut segments comprise a greaterlength relative to the other two angled strut segments within the closedcell.
 19. The medical device of claim 16 where at least one of theclosed cells of the proximal region of the stent comprises four angledstrut segments, where two of the angled strut segments comprise a firstwidth, which is greater than a second width of the other two angledstrut segments within the closed cell.
 20. The medical device of claim15 where the proximal region of the stent comprises a plurality ofproximal apices, where at least one of the proximal apices has an endregion having an integral barb formed therein, where the plurality ofclosed cells of the proximal region of the stent are disposed distal tothe plurality of proximal apices.